Looks absolutely beautiful; but plays like your average, everyday, shovelware cute-mascot-character platformer.
It's a poor imitation of the original Rocket Knight Adventures game: instead of sharp, responsive controls, Rocket Knight suffers from floaty controls and poor hit detection. To be honest, there's little to describe the game other than 'mediocre' - mediocre platforming, mediocre Gradius-style flight sections, mediocre soundtrack (even the remixed first level theme feels weak and listless). The game's definitely beautiful, though, in a charming CGI-cartoon-character kind of way - lots of wacky cartoon contraptions and scenery to be seen.
It's nothing special, but if you have an afternoon to waste ... eh.
 Further thoughts: the game itself recommends that you use a controller; but despite being a console port, all of the button prompts displayed - both in menus and in-game - assume you're using the keyboard, whether or not you are using a controller (tested with a wired Xbox 360 pad). There's no option to re-map controls, either, and the 'Controls' screen only displays the keyboard mappings.
In later sections of the game, you're pitted against enemies with rapid-fire projectile weapons - which, combined with Sparkster's poor manoeuvrability and tendency to fall 'into' enemies, quickly becomes frustrating.
The jetpack mechanic is flawed - rather than recharge at a set rate, it rapidly recharges to about 75% capacity, and then continues to recharge to 100% at a snail's pace. So after performing a platforming section, or two of your three possible offensive moves, you'll be waiting for your bar to slooooowly recharge to full. Pointless.
If you can think of a platforming game sin - blind-faith leaps onto off-screen platforms, tiny platforms located above falls into nothingness, timed platforming sections, enemies with shields or invulnerability while attacking - this game features them.
The enemy AI is terrible - they'll either attack you head-on, or fruitlessly attempt to attack you through the floor.
Finally, the main menu is set up so that the default option when selecting 'Arcade mode' - i.e. the main mode of play - is 'New Game', even if you already have a saved game in progress. It's a minor annoyance, but surely the default option should have been 'Continue'?...